Welcome to HCM! I have gown through your question carefully and from my clinical experince I can say that most common cause of fluid in pleural space, if nothing else is found, is considered to be because of tuberculosis. So, in a way the doctors are doing the appropriate thing by giving her anti TB treatment. It is advisable to start the treatment early in such cases, prolonging it may lead to sticking/ fibrosis in pleural space/ lung. You are right that these drugs give side effect to other organs but when we looks at the risk -benefit ratio of treatment with drug side effects , we decide the line of management. This risk - benefit ratio goes infavor of treatment. Now about the test report, many times on is not able to get to a clear cut pathogen in such cases, as it is difficult to cultivate them in laboratory, also a long time is required some times. but still the consensus says that if the fluid study dosent come out with any bacterial, viral, malignanat cause, it is treated for TB. In almost all such cases the medicine is successful in curing the patient. Hope this answer helps you trust your doctor. give your friend a good, healthy diet, regular walks when she is able to, breathing exercises and get scheduled tests done to check any adverse effect taking place. Please do. it worry about many side effects as anti TB drugs are sometimes given even to newborn / infants and toddlers and they too are able to make it safely. More one can see after one has a detailed list of medicine and the blood test reports of the patient ( which is not mentioned here). Please feel free to ask more questions. Dr. Manisha Gopal.